Recently, the development of downsized high-performance electronic apparatuses is advancing, and the number of input/output signal pins of semiconductor devices is more and more increasing. On the other hand, a demand has arisen for downsizing semiconductor devices. To achieve high-density mounting meeting this demand, the currently prevalent semiconductor package mounting method has changed from a mounting method such as QFP (Quad Flat Package) using conventional leads to a surface mounting method such as BGA (Ball Grid Array) capable of mounting a large number of signal pins at a high density.
The problem of high-density mounting using BGA is to ensure the reliability of a junction portion between a semiconductor package and substrate. More specifically, bumps of individual junction portions are downsized for high-density mounting, and this decreases the junction area and the height of each bump. Since this decreases a margin for absorbing and reducing loads applied to the junction portion, the reliability of the junction portion decreases.
From the viewpoint of loads, junction portions of electronic apparatuses such as a notebook PC and cell phone are damaged little by little by the application of external loads such as impact, vibration, and pressure. If this damage builds up, the junction portions completely break and cause electrical connection defects. Loads are not limited to these external loads. Junction portions are damaged by the application of loads resulting from heat generation and temperature fluctuations when an electronic device is driven in a semiconductor package mounted on a substrate. This is so because there is a difference between the thermal expansion coefficients of the mounted semiconductor package and substrate, so the deformation amounts of the semiconductor package and substrate are different when the temperature fluctuates, and the junction portions absorb this difference between the deformation amounts.
Even when no defect occurs due to one load, a defect occurs due to a repetitive load in many cases. Against this repetitive load, detecting the sign of the occurrence of a defect before damage builds up to cause the defect can be an effective failure prediction method. If the sign of the occurrence of a defect can be detected before the defect occurs, it is possible to take measures, e.g., acquire a data backup and perform maintenance in advance.